1. Field of the Invention
Embodiments of this invention relates to methods for using phosphate and/or nitrate brines to reduce hydrate formation in flowlines under conditions conducive for hydrate formation in the absence of the phosphate and/or nitrate brine. In certain embodiments, the phosphate and/or nitrate brines may include compatible anti-corrosion additives.
2. Description of the Related Art
Gas hydrate is a solid comprising a mixture of water and hydrocarbon gas such as methane. Such mixtures are predominantly water with occluded gaseous hydrocarbons such as methane, ethylene, propylene, etc., normally present in minor amounts. The hydrates may also include other gas components or gas contaminants such as carbon dioxide and hydrogen sulfide. Gas hydrate formation is ubiquitous in offshore drilling for and transportation of resources such as gas and/or crude oil, because subsea temperature and pressure conditions are favorable for or conducive to hydrate formation. In certain environments, the temperature is at or below about 35° F. Thus, wellheads, drilling and production annuli or control lines may become plugged or blocked with an accumulation of gas hydrate. Consequently, drilling fluids may lose their functionality, because hydrate formation may lead to an imbalance in composition of the fluid (less water than originally formulated), increased loss of circulation due to the changes in fluid properties, increased flow back, sudden exposure of the fluids at well surface conditions, which may lead to implosions, and great concern in flow-assurance, as well as real potential of abandoning a well or halting an operation operation are problems familiar to those knowledgeable in the art.
In prior art, gas hydrate is prevented or managed by a number of different methods. One method involves the use of salts and alcohols (glycols, methanol, etc.) (see, e.g., Sloan, E. D. et. al., JPT, December 2009; pp 89-94) to lower a freezing point temperature of the fluid. Other methods involve using low doses of hydrate inhibitors capable of altering hydrate formation kinetics (delaying the rate of hydrate formation) or capable of reducing or preventing hydrate precipitation by keeping hydrate in solution, so-called anti-agglomerants (see, e.g., Proceedings of the 6th ICGH 2008, Vancouver, BC, CA, Jul. 6-10, 2008). Other methods involve managing hydrate agglomeration mechanically by shearing (see, e.g., U.S. Pat. No. 6,774,276; Published International Application No. WO/2007/095399 & United States Published Application 2004/0129609). Other methods involve insulating and heating pipelines to reduce hydrate formation (see, e.g., U.S. Pat. No. 6,070,417). Another method uses high cost organic brines that have a low pour point temperature to reduce or inhibit hydrate formation such as formate brines.
While there are many different methods to address hydrate formation, there is still a need in the art for fluids that reduced or inhibit hydrate formation under conditions conducive to hydrate formation in the absence to the fluids and that are environmentally benign and less costly than fluids known to reduce or inhibit hydrate formation such as expensive formate brines.